Engine emission control systems may include one or more exhaust catalysts such as three-way catalysts, NOx storage catalysts, light-off catalysts, and SCR catalysts. At catalyst light-off temperature (e.g., operational temperature), the exhaust catalyst may oxidize and reduce exhaust constituents in an exhaust gas, thereby converting toxic gases and pollutants in the exhaust gas to less toxic pollutants or inert constituents which are then released into the atmosphere. As an example, when operated between 400° C. and 600° C., a three-way catalyst converts reactive nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (HC) into inert constituents such as diatomic nitrogen (N2), carbon dioxide (CO2), and water (H2O). However, during a cold-start of an engine, when a temperature of the exhaust catalyst is below the light-off temperature (e.g., three-way catalyst temperature falls below 400° C.), the exhaust catalyst may not be able to effectively treat the reactive constituents of the exhaust gas, and as a result, cold-start emissions may increase and the toxic constituents in the exhaust gas may be directly released into the atmosphere.
One way to reduce cold-start emissions is to decrease the time taken by the exhaust catalyst to reach light-off temperatures. As such, to expedite the attainment of the catalyst light-off temperature, engine systems may include heater pumps and/or catalyst heaters to preheat the main exhaust catalysts. One example of such an engine system is provided by Parise in U.S. Pat. No. 5,968,456. Therein, during a vehicle cold-start, a thermoelectric generator is used as a heat pump to heat an exhaust catalyst substrate to reduce the time to exhaust catalyst light-off. In this way, the exhaust catalyst comes up to operating temperature more rapidly, thereby reducing the amount of pollutant emissions at vehicle start-up.
However, the inventors herein have recognized potential issues with such a system. As one example, adding a thermoelectric generator for the sole purpose of heating the exhaust catalyst during the vehicle cold-start may increase manufacturing costs. In addition, such systems may increase packaging requirements and complexity of the engine system. In some cases, these additional heaters may increase exhaust backpressure. Increased exhaust backpressure may lead to increased pumping work, reduced intake manifold boost pressure, cause cylinder scavenging and combustion effects, and further result in turbocharger problems.
In one example, the issues described above may be addressed by a method comprising: during a cold-start, injecting water into an intake of an engine based on a temperature of an exhaust catalyst. As such, water injection systems may already exist in engine systems to cool air charge in the intake manifold, reduce knock, control exhaust temperature and for engine dilution. The inventors have recognized that it may be possible to use the existing water injecting system to inject water into the intake manifold during the cold-start to increase water concentration in the exhaust. By increasing the amount of water injected into the intake manifold, water may be accumulated within the porous material of the exhaust catalyst. As such, the water inside the exhaust catalyst may be used to generate heat within the exhaust catalyst. In this way, catalyst light-off times may be reduced and emission compliance requirements may be met without any additional costs.
As one example, small amounts of water (e.g., light mist) may be injected into the intake manifold when an exhaust catalyst temperature is below a threshold temperature. As an engine speed increases and reaches a threshold speed (e.g., cranking speed), more water may be injected into the intake manifold and as a result, water concentration in the exhaust may begin to increase. Herein, water molecules in the exhaust may start to get accumulated and stored in the porous material of the exhaust catalyst. The momentum of the water molecules stored in the exhaust catalyst may begin to increase. The technical effect of storing water in the exhaust catalyst is the momentum of the water molecules stored within exhaust catalyst may be converted to heat energy within the exhaust catalyst. As a result, the exhaust catalyst may begin to warm up. Further, the water stored in the porous material of the exhaust catalyst may provide additional capacitance to store the exhaust heat. The increased momentum and the increased capacitance may compound together resulting in heating the exhaust catalyst rapidly. Thus, the time taken by the exhaust catalyst to reach light-off temperatures (or catalyst light-off time) may be decreased. By decreasing the catalyst light-off time, cold-start exhaust emissions may be reduced. Overall, the benefits of water injection may be extended over a wider range of engine operating conditions, thereby improving engine efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.